I swapped Barbara her dummy egg for a pair of ducklings, and she settled right down on them. No questions asked. I've been checking every hour in case of 'rejection' but both parties seem happy with the arrangement. I even tried to feel under Barbara, and found a tiny head poking up from under her wing, and was given What For by the new mother. So far so good.
The incubator was quickly washed out and a new batch of eggs set this morning, as a favour to a neighbor. She'll take delivery of those day old chickens, and I expect I will have some of my own Pekin and Barbu d'Uccle eggs to put in there next.